Frequency changer



Nov. 30, 1948. H J. McCREARY v2,455,973

FREQUENCY CHANGER Filed Aug. 15, 1946 2 Shuts-Sheet l FIG.I

FIG. 3

WATTS OUTPUT AT 2O 50 V. II?!" INVENTOR. HAROLD J. M CREARY FIG.6'

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ATTORNEY Pan ma. 30, ms

UNITED STATES PATENT OFFICE FREQUENCY CHANGER Harold J. McCreai-y, Lombard, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application August 15, 1946, Serial No. 690,623

19 Claims. (01. 172-281) This invention relates in general to frequency changers and more specifically to a means for deriving current of one frequency from a source of current of a different frequency. This invention has to do with frequency changers using a variation of the novel core structure as described in two co-pending applications Serial #564,879 filed November 23, 1946, now Patent 2,445,857, issued July 27, 1948, and Serial #597,460 filed June 4, 1945. In particular this frequency changer is adapted to be used to provide a 20 cycle current for signaling purposes in telephone circuits from the usual 60 cycle power lines.

It is an object of this invention to provide an automatic starting frequency changer capable of giving a substantial fiat well regulated output over wide variations of input voltage and load conditions.

Another object of this invention is a frequency changer for converting any commercial power source to the frequency of that power source.

Another object is an improved saturable magnetic core structure of two crossed legs of two types of ferromagnetic metal of different permeability wherein the input windings are placed around the lower permeability leg and the output windings around the higher permeability leg so that at low flux densities the induction between the input and output windings is substantially zero.

A feature of this invention is a method of putting a resonant circuit into oscillation by ap plying thereto a simple rectified pulse from a rectifying means and for repeating the pulse at predetermined time intervals and preventing such pulse or pulses being imparted to the resonant circuit when said circuit is self-sustaining.

A further feature is the utilization of either a relay or a rectifier each to be plugged interchangeably into the same receptacle of the frequency converter to provide starting current.

Another feature is a frequency changer with a rectifier arranged to deliver rectified pulses at intervals to prevent decadence of an overloaded resonant circuit that is operating below the mutual inductance linkage between the primary and the resonant secondary..

Another feature is a frequency changer structure consisting of a small number of components arranged in a compact form requiring a minimum of space and to also be economical to manufacture.

Another feature is-in a frequency changer in which only the primary windings are con-' nected to the alternating power source, all other windings being magnetically and inductively coupled thereto.

Another feature of the invention is a core with a primary coil and a secondary coil wherein their mutual inductance is substantially zero at normal magnetization but which induce odd harmonics at high degrees of saturation although substantially non-inductive to the base frequency of the supply current.

Another feature of this invention is a frequency changer with a starting means which does not unbalance or change the circuit components or structure during starting or at any time.

The exposition of the principles of operation and other features of the invention will be more fully understood and illustrated by the attached drawings in which:

Figure 1 illustrates a magnetic core structure of the new improved frequency changer.

Figure 2 illustrates the fundamental embodiment of the invention including the core structure and windings.

Figure 3 shows a B. H. or magnetization curve indicating the saturation values of the metals and equivalents used in the novel core structure.

Figure 4 shows a modification of the new frequency changer with windings to balance the flux of the core legs.

Figure 5 illustrates a modification of the size of the Allegheny metal leg of the frequency changer core.

Figure 6 is a schematic diagram of one form of the invention with starter.

Figure '7 shows the voltage current wave of the input circuit.

Figure 8 shows the output wave form of the new frequency changer.

Figure 9 is a graphical illustration of the exceptional regulation of the output of the frequency changer when operated with variable loadings.

improved magnetic core structure of two crossed legs consisting of two types of metal of different permeabilities. The laminations in leg desighated AL are of Allegheny electric metal and those of leg designated SI are of silicon iron. These laminations are stacked to form a core that will provide a structure in which one leg is 100% Allegheny electric metal and the other leg 100% silicon iron. In Figure 2 is shown a 60 cycle primary coil wound diagonally through opposite openings of the core and a 20 cycle secondary coil 2 with condenser a attachedwound through the remaining diagonal openings or the core structure. 1

Figure 3 represents the conventional B. l-l. curves oi silicon iron designated Si and the Al legheny metal designated as All. and showing the difference in the saturation point or knee of each metal. This indicates how the relative iiur: densities will vary in the legs of the frequency changer core Figure 2 with primary coil i and secondary coil 2. It is evident that mutual inductance will exist between coil i and coil clue to the diflerence in permeability between the silicon iron Si and the Allegheny metal AL as shown above the snee by the respective curves of Figure 3.

When additional coil turns l--a and i-h llgure i are placed about the silicon leg Si and in series with the primary coil the magnetization flux of the silicon will be brought up to be approximately equal to the Allegheny electric metal at the knee of the curve. This then results in a magnetization flux in the silicon leg as shown by the curve Sl. equivalent of Figure 3. It is evident that the Si equivalent and All curves below the knee are practically equal and there will be practically no mutual inductance below the knee of the curve between the primary and'sec ondary coil. This same effective result can be j 4 limited to any particular theory, he advances the following point by point explanation with graphical illustrations to qualify the aforementioned statements.

Oscilloscope wave traces and operation data from the frequency changer structure as shown in Figure 6 were taken to make a simple quantitative explanation of the operation of this invention. Figure 7 shows the wave traces-of the voltage E and current I of the 6 d cycle input to the prlmary'coil is Figure 8 shows the wave traces of the voltage E and current I of the 2d cycle output of the oscillating secondary coil 2.

, The voltage E contains harmonics of its funda- .ment al which are supported by the coil 6 in series with the oscillating circuit 03 Figure 6 and results in a pleasing ring back tone for use in telephone signalling. The coil 6 could just as achieved without the coils i-e and ih Figure 2'by restricting the "size of the Allegheny metal leg with respect to the silicon iron leg as shown in Figure 5. Energization oi the primary winding will cause it to exert equal magnetizing forces on each of the two legs of the core. If no other magnetizing forces are present, equal fluxes will be produced in the two legs. Since the flux fiowing in these two legs act differentially upon the resonant winding there will be no voltage induced therein.

Now let us assume that an external E. M. F. be momentarily applied to the secondary winding of such value to cause the flux to be raised above the saturation or knee of the B. H. curve. Then the magnetizing forces produced by the current in the primary winding combined with the forces produced by the secondary winding will result in a flux that is mutual to both coils. This flux induces a voltage whose current leads in the secondary circuit at ;3 the frequency of the current energizing the primary circuit. The capacitative' reactance of the condenser 5 of Figure 4 in combination with the secondary winding 2 will cause the current to lead the induced voltage as it flows through the circuit so that it will continue to flow after the above mentioned external E. M. F. source has been removed. Thereafter the secondary cir- -cuit will ocsillate at /3 the frequency of the current in the primary coil l and will absorb energy by mutual inductance from the primary only at times when the core is operating above the saturation point as determined by the frequency of the current in the secondary circuit.

While it is not the wish or the inventor to be total flux threading it.

well be an individual reactance h in series with the oscillating circuit as illustrated in Figure 17.

Retraced Figure ii is the current wave of the 20 cycle output from the secondary coil. This wave also represents the magnetomotive force present in coil 2 oil Figure 6. Let it be assumed that the magnetization curves are composed of straight line sections meeting at the knee or" saturation as shown in Figure 12. The silicon flux curve SI and Allegheny flu curve AL are reversed on the Eli scale to be compatible with the operation of the two crossed legs of the core. Then it the component parts of the current wave Figure ll is projected upon the knee of the magnetization curves Figure 12 along the H axis, and the knee intersection points are again projected baclr to another time scale Figure 13 we have corresponding flux waves representing the approximate flux characteristics of the frequency changer core.

The twenty cycle flux wave blii is representative of the core flux of the Bll/Zllcycle frequency changer when the flux in the two legs are in phase, so that silicon flux SI and Allegheny flux will are additive with respect to the 20 cycle sec ondary coil 2, but in opposition with respect to primary cell i. The voltage in the secondary coil is a function of the time rate of change or" the it follows the flux wave 4:20 of Figure 13 as close as could be expected.

Now when the magnetomotive force wave of I coil z is projected on the knee intersections of the saturation curves SI and oAL of Figure 12 and are again projected on the time scale Figure 13 we have SI and 4 AL flux waves in opposition. It is now evident that these two waves are effective on the primary coil I and it is therefore assumed that the projections could just as well have been projected from the mutual flux curve M Figure 12 to the time scale Figure 15.

This mutual flux curve M Figure'l2 shows how the flux of the 60 cycle primary coil I and the 20 cycle secondary coil 2 changes, or how a magnetomotive force in coil 2 produces a flux within coil i. The characteristics of this curve are very unusual because it is zero during the time when any other normal magnetization curve is changing most rapidly. This means that coils I and 2 are non-inductive to each other at low current 'saturations but become mutually inductive when the Allegheny electric metal becomes saturated. In this invention, mutual induction is produced periodically by the secondary resonant circuit producing core saturation at periodic intervals. Energy to keep the secondary circuit oscillating is transferred during the period when mutual inductance exists. The current in the primary of this invention does not at any time of itself produce saturation of the core.

Figure shows the phase relationship of the mutual flux energy pulses in the core which energize the oscillating secondary. It will now be observed that these pulses are identical to the primary current wave IP shown in Figure 16 a retrace of Figure 7.

The mutual flux wave M (Fig. 12) does not represent the flux that produces the counter voltage EP (Fig. 16) except for very short intervals when there is mutual induction as shown in Figure 15. The flux variations through coil l and through coil 2 are independent of each other at all other times.

The primary magnetization current IP will not produce enough magnetization to permit mutual inductance but when mutual inductance is produced by the oscillating secondary current the primary current rises in value sufficient to overcome the demagnetizing effect of the secondary current only at the odd half cycles.

Figure 17 contains all the embodiments necessary for the operation of the invention and operates fundamentally the same as outlined for that of Figure 4 except for the starter tube 8 and other improvements as follows. The core and windings are similar to that of Figure 4 except for the addition of an output winding l3 inductively coupled to the cycle resonant winding 2, a filament winding 3, a high. voltage starting winding 4, both inductively coupled to the 60 cycle primary winding 4 for supplying filament current and high voltage current to the plate of tube 8 which provides the rectified starting pulses to the 20 cycle resonant winding 2.

If for any reason the 20 cycle resonant circuit including condenser 5, reactance 6 and winding 5 is overloaded or is not oscillating the 20 cyclevoltage in the circuit drops oil? toward zero, the grid 20 to cathode l8 voltage also drops because these two tube elements are connected across part of the resonant winding 2 over leads l6 and H. In the absence of suilicient grid to cathode biasing voltage there will be presented a low resistance path through the tube for the high voltage applied between the cathode l8 and plate l9. The tube I then will fire passing a rectified pulse of current which will be traced from the high voltage winding 4 over lead l5 through a few turns of the resonant winding 2 over lead IE to the cathode l8 through the interelectrode space of the tube to the plate l9, plate lead resistor 9, and over lead l4 to the opposite side of the high voltage winding 4. This rectiiied pulse function of the tube starter will be repeated every /2 cycle until the resonant circuit is self supporting or until part of the 20 cycle voltage is high enough to supply biasing voltage to the grid 20 over lead I! to cause the tube 8 to stop firing.

The regulation time function of the tube 8 is adjusted by proper selections of values for the condenser l2 and the resistors l0 and II. If the resonant circuit is overloaded beyond the mutual inductance point between coils l and 2 the tube 8 will support the resonant circuit with rectified pulses of current every half cycle or 20 pulses a second until the overload "is removed and the resonant circuit becomes self supporting.

In Figure 18 is shown a male plug 22 with an A. C. relay 23 mounted thereon with leads brought out and soldered to prongs I8, 19 and 2| in order to permit the assembly to be plugged into the tube socket of Figure 1'7 as an interchangeable starting means. When the A. C. relay assembly Figure l8'is used in the tube socket of Figure 17 and the resonant circuit is not oscillating or is overloaded there will not be sufficient voltage in the circuit to be extended over leads l6 and I! to terminals l8 and 2|. through the A. C. relay winding 24 to support the armature 24. The armature 24 ,will makeconnections with contact 25 to permit a pulse of current from the high voltage winding 4 to be extended over lead 15 through a few turns of the resonant winding 2, over lead IE to terminal III, through armature 24, contact 25, terminal 19, resistor 9 and lead l4 back to the opposite side of the high voltage winding 4. This voltage pulse introduced into winding 2 restores the resonant circuit so that it is self supporting and the increased voltage in this circuit will be extended over leads l6 and i1, terminals l8 and 2| through the windings of the A. C. relay 23 causing thearmature 24 to pull up away from contact 25 opening the high voltage path to winding 2. The pulse function of the relay starter will be repeated only when the resonant circuit stops oscillating or is overloaded beyond the point of mutual inductance between coils l and 2. The pulse time function will be inherent to the characteristic of each relay so used. The pulse consisting of a number of erratic positive or negative pulses with no regard toward phase relation or polarity.

Figure 6 illustrates a modiflcation of Figure 17 whereby the frequency changer unit is made smaller in physical size and more economical to manufacture. The sign ficant differences are as follows: Only one flux booster winding l-A is used and the harmonic reacter B is wound on one leg of the core 1 instead of a separate element as in Figure 17. The 20 cycle output is taken directly from the resonant winding 2 by means of taps and the high voltage for the starter means is taken from the primary winding l in series with a small booster winding 4. The function of the frequency changer Figure 6 is fundamentally the same as in Figure 17.

Figure 9 is a graph showing the characteristic regulation output to input curves with the variation of the commercial power input volts, volts, 108 volts and volts.

Figurelo is a graphic curve illustrating the maximum 20 cycle output in watts for each value shown of the commercial 60' cycle power supply.

It is believed that these graphs show a decided superiority in regulation over any other prior development in the art.

What is claimed is:

1. In an automatic starting frequency changer, a saturable magnetic core structure consisting of two crossed legs of different permeability, series primary windings disposed diagonally through opposite corners and around the lower permeability leg of the said saturable core structure with a source of alternating current connected thereto, a resonant circuit including a secondary winding disposed diagonally through the opposite corners of the crossed legs of said core structure, a grid controlled rectifier means arranged to supply rectified excitation current pulses to said core with a source of alternating current connected thereto, a resonant circuit including secondary windings encompassing said core wherein electromotive force is transferred from said primary windings to said secondary windings responsive to the saturation or said core members above said flux density point.

3. A frequency changer comprising a saturable core structure of two sections, one section having a higher rate of change or flux density than the other above a certain ilux density value of saturation, a primary winding having a source of alternating current connected thereto, an output winding, an intermediate resonant circuit includ= ing a winding wound about said one core section linking said primary and output windings, and, a condenser connected across said last winding to sustain oscillations therein at a harmonic integrally related to the frequency of said source, a grid controlled rectifier means connected to said resonant circuit whereby rectified excitation current at predetermined time pulses are supplied to said resonant circuit when said one section is below the said saturation point of operation.

4. In a frequency changer, a saturable magnetic core structure consisting of two crossed legs. of diiierent permeability, series primary windings with a source of alternating current connected thereto, said primary windings disposed through opposite corners and around the lower permeability leg; a resonant circuit including a condenser connected across a secondary winding disposed diagonally through the remaining corners and about the higher permeability leg of '7. In a frequency changer, a magnetic core structure including two intersecting members each of a different permeability above saturation, a resonant circuit including a. secondary winding, a primary winding with a source of alternating current connected thereto, said primary winding encompassing the lower flux density member and failing to transfer electromotive force to said resonant winding encompassing said core when the high flux density member is not saturated.

8. In a frequency changer, a saturable magnetic core structure including elements in which the flux densities are different only above a point of saturation, a secondary winding, a, primary wind-- ing with a source of current connected thereto, said primary winding encompassing the lower flux density elements and transferring electromotive force to said secondary winding encompassing said core only when said elements of high flux density are saturated.

' connected across a secondary winding, a terromagnetic core of a plurality of elements oi. equal permeability at saturation and unequal above saturation, mutual induction and the transfer oi electromotive force between said windings occurring only after saturation of said elements. 10. In a frequency changer, a primary winding with an alternating current source connected thereto, a resonant circuit including a secondary winding, a ferromagnetic core structure of two types of metals wherein mutual induction between said primary winding and said secondary winding is produced only by a difference in the degree of magnetization of said two metals above saturation.

11. In a frequency changer, a primary circuit including a primary winding connected to an alternating current source, a secondary winding,

' means including a condenser connected-across of alternating current connected thereto, said permeability leg of said core, a grid controlled rectifier means arranged to provide rectified excitation current pulses necessary to raise magnetization of said higher permeability leg above said saturation point and to thereby efiect mutual inductance between said primary and secondary windings.

6. In a frequency changer, a primary and a secondary winding, 2. core structure common to said windings having two sections of unlike per-' meability, a source of current connected to said primary winding, said primary winding so related to said sections as to cause both sections to reach their saturation points at the same time, said windings so related to said core structure as to cause mutual inductance between the two only after the sections have reached their saturation points.

said secondary winding for making the last winding resonant to a particular frequency, a magnetic core including a plurality of elements having different degrees of flux density above a common knee of saturation, said elements linking said windings only above said knee of saturation to thereby produce mutual inductance between said windings.

12. In a frequency changer, a resonant circuit including a secondary winding, a primary circuit including a winding with a source of current connected thereto, a magnetic core structure including two types of ferromagnetic material of difierent permeability linking magnetically said primary circuit with said resonant circuit wherein mutual inductance between said circuits is produced by the difference in the degree of magnetization of said materials.

13. In a frequency changer, a primary and a secondary winding and an alternating current source, a circuit for the said primary winding including said source, a circuit for the said secondary winding including a condenser connected across said winding. for making the last circuit resonant to a particular frequency, a magnetic core linking said circuits having elements of different permeability, said elements having different degrees of magnetization above saturation to thereby produce mutual induction between said windings only after said elements are saturated.

14. A frequency changer comprising a saturable core structure including two crossed legs each of a different flux density with certain degrees of magnetization providing diflerential flux paths linking an energized primary winding to a secondary winding whereby mutual inductance and the transfer of electromotive force between said windings occurs only after saturation of one of said legs within said secondary winding.

15. A frequency changer comprising a core structure of two crossed legs each of different flux density with certain degrees of magnetization and having two flux paths linking a primary winding including a power source to a secondary winding, an output winding inductively coupled to said secondary winding, a resonant circuit composed of said secondary winding with a condenser connected across said winding to sustain oscillation therein at a harmonic integrally related to the frequency of said source.

16. In a frequency changer, a saturable magnetic core structure of two types of ferromagnetic material disposed within a secondary winding and a primary winding, a source of alternating current connected to the primary winding, a resonant winding encompassing said core, said primary winding inductively coupled to said resonant winding only after saturation of said core by said secondary winding.

17. An automatic starting frequency changer comprising a primary winding and a resonant circuit including a secondary winding, each of said windings disposed about a magnetic core, a grid controlled rectifier means arranged to provide rectified excitation current at predetermined time intervals to said resonant circuit when said circuit falls below a point of self sustained oscillation.

18. A frequency changer comprising a primary winding with an alternating current source connected thereto, a resonant circuit including a condenser connected across a secondary winding, a saturable core. structure including two crossed legs each of a diiIerent flux density providing therein difierential flux paths linking said primary winding to said secondary winding in such a manner that a transfer of electromotive force between said windings occurs upon saturation of the leg within said secondary winding to thereby maintain oscillation at V3 the frequency of said source in said secondary winding.

19. An automatic starting frequency changer comprising a primary winding and a resonant circuit including a secondary winding, each of said windings encompassing a common magnetic core linkage, a rectifier means coupled between said primary and said secondary windings, said rectifier means disposed to supply rectified excitation current in pulses to said secondary winding at such times when said resonant circuit is not self sustaining.

- HAROLD J. McCREARY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,088,620 Stocker Aug. 3, 1937 2,418,641 Huge Apr. 8, 1947 

